1. Field of the Invention
The present invention relates to a vibration actuator for relatively moving a contact body by a vibration produced in a vibrator.
2. Related Background Art
FIGS. 10A and 10B are sectional views of a rod-shaped ultrasonic wave motor described in U.S. Ser. No. 340,469 as the prior art of the present invention. A vibration member 1 generates an oscillating vibration upon application of AC voltages to a piezoelectric member 3, and the surface particles of a sliding portion B make an elliptic motion. On the other hand, a movable member 2 is in press-contact with the sliding portion B and receives a frictional driving force from the vibration member. At this time, a friction layer 1a on the vibration member side is an Ni-P-SiC composite galvanized layer, and is formed on the entire surface of the vibration member 1.
In this prior art, the function required of the friction layer is given by the composite galvanized layer. However, the galvanized layer must be formed on a portion that is not associated with the required function. When the galvanized layer itself can be uniformly and smoothly formed on the entire surface, this problem is concluded as only a wasteful treatment. However, a post-treatment is required after the galvanizing treatment due to the nonuniformity of the thickness, surface roughness, and warp of the galvanized layer. As a first example, since a sliding layer 1a' of the vibration member must effectively receive a minute displacement of the piezoelectric member, it must be finished to have a surface precision as high as that obtained by cutting or grinding. Thus, the sliding surface is subjected to lapping after the galvanizing treatment, in practice. The same applies to an actuator of a type in which a piezoelectric member is adhered to a vibration member. As a second example, since the resonance frequency of a vibration mode used for frictional driving must fall within a predetermined range, the galvanized portion must be removed in the post-treatment. More specifically, in the prior art shown in FIG. 10, the galvanized layer attached to a constricted portion 1d' of the vibration member 1 must be locally removed to adjust the resonance frequency to a predetermined value. This process is discussed in detail in Japanese Laid-Open Patent Application No. 5-300768, and a detailed description thereof will be omitted.
On the other hand, some attempts have been made to utilize a resin, rubber, or the like as the friction layer. However, with this method, since the resin or rubber has a low rigidity, a molded member consisting of such a material cannot maintain a predetermined shape, and it becomes difficult to maintain high positional precision if such a member is coupled to the vibration member. On the other hand, when the molded member whose rigidity is increased by increasing its thickness is coupled to the vibration member, since the resin or rubber has large vibration attenuation, the energy loss of the motor becomes undesirably large.